My little boat leaks but can't find the source?

[olfellow]

This summer i made a small stitch and glue boat from plywood.
I used glass fiber strips to strengthen the joints and covered the entire hull with one fiber glass cloth, both with epoxy.
After that i rolled a layer of clean epoxy on the outside and this inside.

Last week i took the boat for a few rowing trips. Yesterday i noticed a few drops of water entering the boat through the stitch and glue holes.


I first looked at the outside to look for visible damage. no damage and no open stitch and glue holes. But i saw this:

it's a outside edge covered with glass fiber strip and the next layer is a fiber glass cloth, the next layer (the clean epoxy) didn't fully "cover" the edge.

Is it possible that water enters this way?
If not is there maybe a trick to detect or see where water enters?

I suspect water enters somewhere, goes through the layers of plywood, drips down due gravity and leaves at the lowest point.

 

[BlueBell]

Congratulations on your build and welcome to the forum.

The holes should all have been filled with thickened epoxy and covered with epoxy fiber-tape and resin.

In leaks like this water can travel in ANY direction, not necessarily following gravity.

You'll want to dry the area as well as possible and then dry it chemically before repairing.

Also, run a strip of fiber-tape on the inside too.

 

[Mr Efficiency]

Lie under the boat and place a strong light inside it, look for any signs of light. Oh, and wait till night-time !

 

[olfellow]

Cheers guys for the helpful replies.
I now highly suspect that the photographed edge is the problem, above and below the wood had turned a bit black (above the edge cause the boat is transported and stored upside down). The edge is near 160 degrees and was quite difficult to cover with thickened epoxy and i suspect the thickened epoxy didn't reach the outside. I can also remember i ran out of epoxy while doing this edge. A good lesson learned

But that means that only fiber glass strips and/or cloth (with epoxy) doesn't make a watertight seal. Can anybody confirm this?

In the meantime i took the my trusty sander and sanded to the glass fiber and rolled 2 layers of epoxy on the troubled area. I didn't go the "right way" because i do want to redo the transom, with a transparent material, when the weather gets worst.

 

[rwatson]

"But that means that only fiber glass strips and/or cloth (with epoxy) doesn't make a watertight seal. Can anybody confirm this?"
statement.

I guess that is because you

"I used glass fiber strips to strengthen the joints and covered the entire hull with one fiber glass cloth, both with epoxy.
After that i rolled a layer of clean epoxy on the outside and this inside."

But, I bet what you didnt do was use several layers of Epoxy. You cant get a totally waterproof job with one layer of Epoxy.

The best technique, shown on many videos, is to squeegee off the initial wetting out, and then when it has started to harden, apply the second coat.

This guy explains it well

 

[olfellow]

Cheers @rwatson !
I honestly thought after the fiber glass cloth with epoxy you only needed one layer of epoxy.

Now I'm thinking i must have been quite lucky the little boat didn't sink, i did make quite a few rowing trips even with storm.

Time to bring out the sander again and apply 2 more layers of epoxy on the entire hull.

Thanks again for avoiding me wet clothes in the future!

 

[Rumars]

I see two big mistakes in the photos. One are the unfilled holes. When you applied fiberglass over them those holes sucked the epoxy out of the cloth creating dry spots. The second photo shows the bigger problem. Your outside corners are not filled and rounded. The gap sucked the epoxy, the cloth got starved, and beeing over a sharp edge imediatly fractured. There is no watertightness there. You can clearly see the white dry spots showing the fiberglass structure in both photos. The solution is to grind the offending spots to wood, fill with thickened epoxy, sand the corners round and apply new fiberglass patches. If the whole chine is like that (not rounded over) I would sand everything round and apply fiberglass tape over the whole lenght of the joint.

 

[olfellow]

Thanks @Rumars !
Very interesting tips on how to improve my stitch and gluing skills, i will sure be applying them in a few weeks when i repair/fix the made mistakes.
I do think it's a bit strange that this is the only edge/corner that has trouble, but all other corners are indeed more rounded and better filled.
Learning while building